The present invention relates generally to a diagnostic medical imaging apparatus and more particularly to a mammography machine that employs a near-infrared laser as a radiation source.
Cancer of the breast is a major cause of death among the American female population. Effective treatment of this disease is most readily accomplished following early detection of malignant tumors. Major efforts are presently underway to provide mass screening of the population for symptoms of breast tumors. Such screening efforts will require sophisticated, automated equipment to reliably accomplish the detection process.
The x-ray absorption density resolution of present photographic x-ray methods is insufficient to provide reliably early detection of malignant tumors. Research has indicated that the probability of metastasis increases sharply for breast tumors over 1 cm in size. Tumors of this size rarely produce sufficient contrast in mammogram to be detectable. To produce detectable contrast in photographic mammogram, 2-3 cm dimensions are required. Calcium deposits used for inferential detection of tumors in conventional mammography also appear to be associated with tumors of large size. For these reasons, photographic mammography has been relatively ineffective in the detection of this condition.
Most mammographic apparatus in use today in clinics and hospitals require breast compression techniques which are uncomfortable at best and in many cases painful to the patient. In addition, x-rays constitute ionizing radiation which injects a further risk factor into the use of mammographic techniques as most universally employed.
Ultrasound has also been suggested, as in U.S. Pat. No. 4,075,883, which requires that the breast be immersed in a fluid-filled scanning chamber. U.S. Pat. No. 3,973,126 also requires that the breast be immersed in a fluid-filled chamber for an x-ray scanning technique.
U.S. Pat. No. 5,692,511 discloses a laser imaging apparatus.
In recent times, the use of light and more specifically laser light to non-invasively peer inside the body to reveal the interior structure has been investigated. This technique is called optical imaging. Optical imaging and spectroscopy are key components of optical tomography. Rapid progress over the past decade have brought optical tomography to the brink of clinical usefulness. Optical wavelength photons do not penetrate in vivo tissue in a straight line as do x-ray photons. This phenomena causes the light photons to scatter inside the tissue before the photons emerge out of the scanned sample.
Because x-ray photon propagation is essentially straight-line, relatively straight forward techniques based on the Radon transform have been devised to produce computed tomography images through use of computer algorithms. Multiple measurements are made through 360xc2x0 around the scanned object. These measurements, known as projections, are used to backproject the data to create an image representative of the interior of the scanned object.
In optical tomography, mathematical formulas and projection techniques have been devised to perform a reconstruction function somewhat similar to x-ray tomography. However, because light photon propagation is not straight-line, techniques to produce cross-section images are mathematically intensive and invariably require establishing the boundary of the scanned object. Boundary determination is important because it serves as the basis for reconstruction techniques to produce interior structure details. Algorithms to date do not use any form of direct measurement technique to establish the boundary of the scanned object.
Photon propagation through breast tissue does not follow a straight line and can best described as xe2x80x9cdrunkard""s walkxe2x80x9d. The mean free path of a photon within the breast is on the order of 1 mm, and after this short distance the photon is deflected at a different direction. In general, the photons are said to be forward scattered with the mean of the cosine of the scattering angle on the order of 0.9. The index of refraction of breast tissue is approximately 1.5 and thus the speed of photon travel within the breast is on the order of 2xc3x97108 meters per second.
In accordance with the present invention, knowledge of the propagation of light through the breast tissue, determination of the perimeter of the breast at the selected scanning location, and the known configuration of the scanner allow a method of selecting those photons that travel the shortest path through the breast to be used to produce a computed tomography of the interior of the breast.
It is an object of the present invention to provide a detector array that can detect the significantly different light levels emerging from a scanned object.
It is another object of the present invention to provide a processing circuit for a detector that can accommodate the dynamic range of the detector.
It is still another object of the present invention to provide a detector with multiple gain amplifier to accommodate the dynamic range of the detector signal, which could range in relative amplitude from approximately 10xe2x88x9211 to 1.
It is another object of the present invention to provide a processing circuit that can detect the earliest arriving photons exiting from the breast being scanned.
It is another object of the present invention to acquire data to allow reconstruction of contiguous cross-section images of the interior of a breast using short pulses of near infrared light.
It is an object of the present invention to provide a direct determination of the boundary of the scanned object, thus eliminating a significant portion of the time required to reconstruct an interior image of the scanned object.
It is another object of the present invention to provide one or more sensors placed on the same side of the scanned object as the impinging radiation to detect the location of the point of contact of the impinging beam on the scanned object and using this information to determine the boundary of the object.
It is another object of the present invention to provide a means for directing a laser beam into the breast by use of a fiber optic cable and to couple light collected by a collimator to a photodetector.
It is another object of the present invention to provide a means by synchronizing the data acquisition circuits to the arrival of photons delivered through fiber optic cable and optics.
It is another objective of the present invention to provide processing circuit to allow acquiring data to determine the TPSF for each scan location, and use the TPSF to estimate the transport scattering coefficient, xcexcsxe2x80x2, and the absorption coefficient, xcexca.
It is still another objective of the present invention to provide data for imaging reconstruction through use of all or time-gated portions of the TPSF data.
In summary, the present invention provides a detector array for a laser imaging apparatus, comprising a plurality of detectors disposed in an arc around an opening in which an object to be scanned is disposed; and a multi-gain amplifier circuit connected to each detector.
The present invention also provides a detector array for a laser imaging apparatus, comprising a plurality of detectors disposed in an arc around an opening in which an object to be scanned is disposed; and a multi-gain amplifier circuit means for processing the output of each detector to provide data for use in image reconstruction.
The present invention further provides a photodetection circuit for use in a laser imaging apparatus, comprising a photodetector adapted to respond to a laser pulse exiting from a breast being scanned; a multi-gain preamplifier circuit connected to the output of the photodetector; a switch connected to the output of the multi-gain preamplifier for sampling the output of the photodetector; an RC circuit for spreading the sampled signal; an amplifier connected to the output of the RC circuit; and an integrator for integrating each sample of the output. A time-gating circuit is operably connected to the switch to open and close the switch at regular intervals of time during the occurrence of the output. A laser pulse synchronization circuit is operably connected to the time-gating circuit to provide a signal to the time-gating circuit as to when the laser pulse is expected to arrive at the photodetector.
The present invention still provides a method for collecting data for use in image reconstruction of an object being scanned, comprising providing a plurality of detectors disposed in an arc around the object to be scanned; connecting a multi-gain amplifier circuit to each detector; impinging a laser beam at a point on the object; sampling the output curve of each detector in sufficient time intervals to recreate the curve; integrating each sample; repeating the sampling and integrating for a number of laser pulses; recording each output for each pulse for use in image reconstruction; orbiting the detectors and the laser beam to another point on a circle; and repeating the above until a complete circle has been traversed.
The present invention also provides an apparatus for determining the perimeter of an object being scanned, comprising a scanning chamber for receiving therein an object being scanned; a source of laser beam disposed within said scanning chamber for impinging on the object being scanned, said laser beam being adapted to orbit around the object; an array of sensors disposed within said chamber, each of said sensors being adapted to detect light reflecting from the surface of the object due to said laser beam exiting from the object; each of said sensors being disposed such that at least only one of said sensors generates a peak response to light emanating from a point on the surface at a predetermined distance from a reference point, such that at each angular position of said laser beam in the orbit, a specific point at a distance from the reference is determined, thereby to generate a set of points representing the perimeter of the surface after a complete orbit.
These and other objectives of the present invention will become apparent from the following detailed description.